I Tweeted this but I'll repeat it here; I would imagine a high percentage of these downloads (50%?) were users who 'unwittingly' downloaded Safari 4 while downloading updates to other Apple software like iTunes and Quicktime.

Apple's attempt at 'bundling' Safari with every iTunes update is quite annoying personally but it sure helps to inflate those download numbers.

Also does this number count 'upgrades' from Safari 3?

.. off to RTFA